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Earth Surface & Interior

A major scientific challenge highlighted in the SESWG report is to observe the interactions among ice masses, oceans, and the solid Earth, and to understand the implications for sea level change. Meeting this challenge requires the realization of a stable International Terrestrial Reference Frame (ITRF) at sub-millimeter accuracy. ITRF2005 and ITRF2000 have inconsistencies along the polar (Z) axis which are much greater than along the equatorial axes (X, Y). Similar larger systematic errors in Z plague GPS inversions for geocenter motion. The primary cause of bias is the uneven site distribution between the Northern and Southern Hemispheres. We propose a new approach to solving the bias problem, based on the fact that estimates of degree-1 crustal motion depend on the realization of the reference frame. An imperfect network creates an anisotropic reference frame with an artificially preferred direction for geocenter motion. Our approach is to treat a realizable imperfect frame as an independent type of frame, rather than as an approximation to a perfect frame. By using the appropriate displacement model, the systematic biases associated with degree-1 deformation can be greatly reduced. We have developed a new elastic loading theory, with degree-1 load Love numbers that are polarized as a result of an imperfect frame. Numerical simulations with hypothetical loading scenarios have illuminated the source of the Z-problem in GPS inversions. By using the appropriate Love numbers for each, our scheme works for geocenter estimates for both SLR and GPS networks. We propose a series of tests to quantify the improvement in ITRF stability. We also propose to implement our method to estimate geocenter motions on sub-seasonal time scales based on SRL, GPS, and combined networks. We plan to apply our new method to deriving monthly degree-1 coefficients for the GRACE gravity time series.

Project PI: Bradford Hager/ Massachusetts Institute of Technology

54-622 Dept. of Earth, Atmospheric, and Planetary Sciences Massachusetts Institute of Technology 77 Massachusetts Ave. Cambridge, MA 02139-4307 USA

Phone: (617)253-0126

Email:  brad@chandler.mit.edu

http://eapsweb.mit.edu/people/person.asp?position=Faculty&who;=hager

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Started: Aug 09, 2010

Last Activity: Dec 10, 2010

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